1. Field of the Invention
The invention relates to an AC/DC converter comprising a resonant converter.
Such AC/DC converters are used for converting an alternating voltage into a direct voltage in, for example, television apparatuses or discharge lamps in the form of switched-mode power supplies so as to convert a line voltage into a DC power supply voltage.
2. Description of the Related Art
An AC/DC converter which loads a public AC voltage line is subject to particular requirements as regards the current which may be taken from the AC voltage line. For example, the current taken up by the AC/DC converter may customarily have only a limited harmonic part, i.e., the AC/DC converter should essentially operate as an active resistance. The impedance part of the input impedance of the AC/DC converter should not exceed given values. Such requirements are further specified in, for example, IEC 1000-3-2.
It is known from the book by Udo Leonhard Thiel "Professionelle Schaltnetzteilapplikationen", Franzis-Verlag, 1996, chapter 3.9, to use resonant converters for increasing the power density of switched-mode power supplies (the ratio between output power and apparatus volumes). It is based on the recognition to include an LC resonant circuit in the primary circuit of a switched-mode power supply, which, when necessary, is charged for a given time interval and discharged again in the same time interval. Power supplies realized by means of a resonant converter have a smaller volume, an improved reliability and reduced EMV emissions.
Various topologies for resonant converters with half-bridge circuits are known from the thesis by Robert L. Steigerwald "A Comparison of Half-Bridge Resonant Converter Topologies", IEEE Transactions on Power Electronics, vol 3, no. 2, April 1988, pp. 174 to 182.